Rule: no-eq-null

The `no-eq-null` rule flags comparisons to null that do not use a type-checking operator.

Comparing to `null` without a type-checking operator (`==` or `!=`), can have unintended results as the comparison will evaluate to true when comparing to not just a `null`, but also an `undefined` value.

```js
if (foo == null) {
  bar();
}
```

This rule provides the functionality of JSHint's **eqnull** rule.